ИСТИНА

Analysis of a global avian dataset showed that summer basal metabolic rate (BMR) of long-distance migrants is higher than that of non-migrants. There are two alternative explanations to this finding: 1) The high BMR in migratory species reflects elevated maintenance costs of metabolic machinery for long-distance migration; 2) The high summer BMR of migrants reflects the negative correlation between ambient temperature and BMR because long-distance migrants generally breed at higher latitudes than non-migrants. At the same time, information on BMR of long-distance migrants at their wintering grounds in tropics is scarce. To fill in this knowledge gap, we measured BMR in 17 species of passerine migrants from southern Vietnam, as well as BMR in 51 species of passerine residents and 35 species of non-passerine residents. In a phylogenetically controlled analysis we showed that migratory birds had higher BMR than both groups of residents. Taking into account the high rate of BMR adjustment in laboratory acclimation studies, the higher BMR of migrants on their wintering grounds was more likely related to energetic demands of long-distance migration than to preadaptation to lower temperatures on their breeding grounds.